How to apply the exchange rate to the slip from FXWorksheet?

When you open a T5 , T3 or Foreign form, you select the currency from there and the exchange rate will be filled by the program

Mario is correct.  On - for example - the "Foreign Income" page, the top line asks for the currency.  You click on the arrow to the right and a list of currencies pops up.   Scroll down to the one you want and the exchange rate is automatically populated.  

Jo